The coefficient of kinetic friction is mk the normal force is F n Kinetic friction formula is handy for questions to compute the friction amid the bodies which are in motion. Thus the ratio of friction F to load L is constant. When a body press against a surface the surface deforms even if it appears to be rigid.
Friction is a force much like a pull.
It is a scalar quantity which implies that the direction of the force shall not affect the physical quantity. The deformed surface pushes the body with a normal force R that is perpendicular to the surface. Now that the fridge is sliding there will be a kinetic frictional force exerted on it. The frictional force is eqmu N eq where eqmu eq is the coefficient of friction.